Varactor-tuned dual-band filter with constant absolute bandwidth

This paper proposed a novel varactor-tuned dual-band filter with constant absolute bandwidth. It is composed of a pair of half-wavelength open-ended resonators and a pair of quarter-wavelength short-ended resonators. The resonators utilized two different methods to control the electric and magnetic coupling so as to achieve constant absolute bandwidth. A dual-band tunable filter is designed, and the measured results of the filter illustrate the effectiveness of this design method.